1. Technical Field of the Invention
This invention relates to roll casting of molten metal. More particularly, this invention relates to improvements in apparatus controlling the flow of molten metal from a reservoir to a rolling mechanism.
2. Background Art
The processing of molten metal by continuous casting to convert it to plate or sheet fabricatable into various shapes conventionally involves the delivery of molten metal to a pair of rollers from a casting nozzle comprising an elongated nozzle tip.
Process economics would justify the continuous casting and subsequent rolling of wide sheets, i.e., over 40 inches in width, as well as faster rolling speeds, i.e., 200 lb/in/hr. However, shortcomings in nozzle tip design resulting in nonuniform molten metal temperature and exit velocities of the molten metal entering the nip of the rollers have prevented use of such widths and speeds.
These problems in nozzle tip design, including nonuniform metal flow velocity profiles across the nozzle tip and nonuniform temperature distribution, as well as flow disturbances adjacent the side risers of the nozzle and any spacers which may be present within the nozzle, can result in hot spots in roll caster and consequently cause bleed out at high speed casting. Furthermore, flow disturbances and separation caused by the internal structures of the nozzle tip can cause surface defects on the resulting cast plate or sheet. The latter condition of flow disturbances is particularly complicated by the necessity of utilizing some sort of spacers to support the top wall of the nozzle and to maintain uniformity of spacing between the top wall and bottom wall of the nozzle when attempting to cast wide plate or sheet by continuous casting techniques.
In the prior art, regulation of metal flow has been attempted using divergent channels which may contain baffles. For example, Chateau et al U.S. Pat. No. 4,153,101 provide a nozzle having a lower plate and upper plate separated by cross pieces and side end portions which are divergent along at least a portion adjacent the end of the nozzle.
Blossey et al U.S. Pat. No. 3,799,410 show a feed tip having baffles therein which coact in controlling the direction of flow of molten metal through the cavity in such a manner said to insure continuous distribution of molten metal to the nozzle uniformly throughout its length.
However, the control of the metal flow velocity as well as uniform temperature distribution within the nozzle, particularly when a wide casting strip is desired, has been found to involve design criteria which are not satisfied by the prior art.